Coriolis Ocean database for ReAnalysis CORA3 Documentation V 1.0 Cécile Cabanes, Antoine Grouazel, Christine Coatanoan, Victor Turpin December 2, 2011 IFREMER - Pointe du Diable -29280 Plouzané - web: www.coriolis.eu.org/Science/Data-and-Products Contents 1 Dataset overview 1 1.1 History of the dataset .................................... 1 1.1.1 Previous versions of CORA ............................. 1 1.1.2 Main changes for the CORA3 version ....................... 1 1.2 Data sources ......................................... 2 1.3 Organisation of the dataset .................................. 2 1.3.1 Files formats - structure ............................... 2 1.3.2 Type of files and data type .............................. 3 1.3.3 The Index files .................................... 3 1.4 Data quality ......................................... 4 1.4.1 Quality flags ..................................... 4 1.4.2 Adjusted parameter versus parameter ........................ 4 1.4.2.1 Particular case of pressure correction for Argo floats ............ 5 1.5 Goals and uses of the dataset ................................ 7 1.5.1 Research ....................................... 7 1.5.2 Ocean model validations .............................. 7 1.5.3 Data assimilation in ocean models ......................... 7 2 Description of data processing 9 2.1 Data flow ........................................... 9 2.2 Quality checks ........................................ 10 2.2.1 Real-time and Near-real-time channel ........................ 10 2.2.2 CORA channel .................................... 10 2.2.2.1 Systematic test on new and updated data ................... 10 2.2.2.2 Tests on the whole database ......................... 10 2.3 Elimination of duplicate profiles .............................. 10 2.4 XBT bias correction ..................................... 12 3 Description of the dataset 15 A Tables 43 i CHAPTER 1 Dataset overview 1.1 History of the dataset The program Coriolis has been setup at Ifremer at the beginning of the 2000’s in the wake of the devel- opment of operational oceanography in France. The project was launched in order to provide ocean in situ measurements to the French operational ocean analysis and forecasting system (Mercator-Océan) and to contribute to a continuous, automatic, and permanent observation networks. The Coriolis data centre has been set up to gather, qualify [4] and distribute data from the global ocean both in real and delayed time. The Coriolis database is a real time dataset as it is updated every day as new data arrive. On the contrary, the CORA database corresponds to an extraction of all in situ temperature and salinity profiles from the Coriolis database at a given time. All the data is then re-qualified. CORA is meant to fit the needs of both re-analysis and research projects. However, dealing with the quantity of data required by re-analysis projects and the quality of data required by research projects remains a difficult task. Several important changes have been made since the last release CORA02, both in the production procedure (to be able to release yearly reanalysis) and quality checks applied to the data. These changes are fully described in this document. 1.1.1 Previous versions of CORA Two previous versions of CORA have already been released by the Coriolis data center: CORA01 in 2007 and CORA02 in 2008. CORA01 contains data from 2002 to 2006 while CORA02 is from 1990 to 2007. To produce such a dataset the Coriolis data center proceeded basically in three steps: 1. Data passed through a statistical quality check based on objective analysis method (see [6] for further details).This statistical check produced alerts on doubtful profiles. 2. All doubtful profiles were visually checked, and profiles were flagged - if necessary - in the Cori- olis database. 3. Data was extracted from the Coriolis database (to produce netcdf files). 1.1.2 Main changes for the CORA3 version • A new procedure is now used to produce the dataset: This procedure fully described in section 2.1 was set up to be able to extract only new and updated data from the Coriolis database at each new 1 CORA3 Documentation, Rev. 1.0 release of CORA. • A new set of quality checks is performed on the data. These quality checks are described in section 2.2 • A check of duplicates was re-run on the whole dataset (see section 2.3) • An XBT bias correction has been applied. This correction is described in section 2.4 • The CORA3 release has been extended for the period 1990-2010. 1.2 Data sources Data submitted to, or obtained by, the Coriolis Data Centre which contains profiles of temperature and/or salinity were potential data source for CORA3 database. The CORA3 database thus corresponds to the Coriolis database at the date of the CORA3 retrieval. For CORA3, the data retrieval has been spread over time (see table 1.1). Data Span Date of retrieval 1990-2008 25-May-2010 2009 09-September-2010 2010 22-03-2011 Table 1.1: Dates of retrieval for CORA3 The Coriolis centre receives data from Argo program, French research ships, GTS data, GTSPP, GO- SUD, MEDS, voluntary observing and merchants ships, moorings, and the World Ocean Database (not in real time for the last one and for CTD only). CORA thus contains data from different types of instru- ments: mainly Argo floats, XBT, CTD and XCTD, and Mooring. 1.3 Organisation of the dataset 1.3.1 Files formats - structure Files structure is the same as for the distribution of the Argo profiles data and it is fully described in the argo-dm-user manual, section 2.2. Each netcdf files contains N_PROF profiles and a profile contains measurements of different variables (e.g. temperature, salinity) performed at N_LEVELS different pres- sures or immersion taken as the instrument is being dropped or risen vertically in the water column. For surface-only data, the profile consists of a single measurement. For moored buoys and drifting buoys, a profile is a discrete set of concurrent measurements from the instruments placed at different depths. All the variables in a file are defined for Argo float profiles, but most of these variables still have the same signification for other types of profile (e.g. XBT or CTD profiles). Guidance for the users Each profile has a unique identifier in the Coriolis database and the CORA database which is the DC_REFERENCE number. Please, refer to this DC_REFERENCE number if you want to make a feedback on a specific profile to the Coriolis data centre. The variable PLATFORM_NUMBER is the platform identifier that is assigned for the life of the platform (e.g. Profiling floats, moored buoys, ...). For measurements collected from research vessels or merchant ships-of-opportunity the PLAT- FORM_NUMBER is the vessel/ship identifier. 2 Chapter 1. Dataset overview CORA3 Documentation, Rev. 1.0 1.3.2 Type of files and data type The data are stored in 7 netcdf files types: PF, XB, CT, OC, MO, BA, and TE. Files are stored in yearly directories. There is one file per day and per type. The file name is of the form: CO_DMQCGL01_YYYYMMDD_PR_TT.nc This file contains all the raw data of the date YYYYMMDD and of the data type TT. • PF files : data from Argo floats directly received from DACS (real Time and delayed mode if available). These data have a nominal accuracy of 0.01° and 0.01 PSU and are transmitted with full resolution. • XB files : XBT or XCTD data received from research and opportunity vessels have accuracy within 0.03° to 0.1° for temperature and 0.03 to 0.1 PSU for salinity. • CT files : contains CTD data from research vessels (accuracy on the order of 0.002° for tem- perature and 0.003 PSU for salinity after calibration) but also data from sea mammals equipped with CTD (accuracy is on the order of 0.01° for temperature and 0.02 PSU for salinity but can be lower depending of the availability of reference data for post-processing, see [1]) and received from MNHN and some sea Gliders. • OC files : Others CTD and XCTD data coming from the high resolution CTD dataset of the World ocean database 2009. • MO files : Mooring data are mostly from TAO TRITON RAMA and PIRATA mooring and have accuracy generally comparable to Argo floats (except for S near surface). • TE and BA files : The two last categories are for all the data transmitted trough the GTS (data from Argo floats not yet received at the DACS, mooring, XBT,...). This transmission system imposes limitation on the accuracy: data is truncated two and one places beyond decimal point for TE and BA type respectively. Guidance for the users : How to find a particular data type in CORA3? This classification of the data in netcdf files depend mainly on the data sources and resolution. However, it can be difficult for the user to find all the data from one type of instrument (e.g. CTD) as it is found in different types of files (e.g. CT, OC, TE files for CTD instruments). The variable WMO_INST_TYPE in the netcdf raw files can help to distinguish the different instrument types (see table A.1). How- ever the same WMO_INST_TYPE can be attributed to different types of instrument platform (e.g. the WMO_INST_TYPE 830 standing for CTD is attributed to CTD launched from vessels or ships, CTD attached to sea mammals, some mooring buoys etc...). To facilitate the identification of a particular type of data a PROBE_TYPE code was attributed to each profile (see table A.2 for definition of codes). The PROBE_TYPE variable can be found in the Index files (see section 1.3.3) and be used to select a particular type of data. 1.3.3 The Index files An Index for the raw data of CORA3 is available (./RAW/Index). The index is organized as follow: There is one index file per month (e.g.